As disclosed in a Japanese patent document JP 2008-40240 A (Patent document 1), an optical scanner having a following configuration is proposed, in which a forced scanning section, a resonance scanning section, a mirror part, and a fixed part are provided, and among which the mirror part is supported by the resonance scanning section and the resonance scanning section is supported by the forced scanning section. In such an optical scanner, an image formation position of the mirror part is scanned in two dimensions, according to an applied voltage to a piezoelectric film in the forced scanning section and the resonance scanning section.
More practically, the resonance scanning section is formed of an actuator part and a beam part, and the actuator part and the mirror part are connected by the beam part. Further, in such structure, the voltage is applied to the mirror part via the actuator part and the beam part, and the mirror part is driven at the resonant frequency that is based on a natural frequency of the beam part.
The optical scanner described above is capable of scanning the image formation position in two dimensions, and may be configured to scan the image formation position in three dimensions (3D). For example, a 3D image scanning apparatus may be realized by using a variable focus mirror part, (e.g., by using a piezoelectric film) as the mirror part.
More practically, a variable focus mirror (a vari-focal mirror) may have a layered structure, in which a conductive base material supports a piezoelectric film and a mirror electrode and an electric potential difference is caused between the mirror electrode and the conductive base material, thereby applying a voltage to the piezoelectric film and varying the focus of the mirror part. Such a structure is easily manufactured by using a semiconductor manufacturing process for laying the piezoelectric film and the mirror electrode on the conductive base material.
Here, when making a 3D scanning optical scanner according to the above-described structure, a mirror driving wire connected to a mirror electrode for a voltage application to the piezoelectric film of a vari-focal mirror passes the resonance scanning section that surrounds the mirror part.
More practically, the mirror driving wire extends (i) from the forced scanning section outside of the resonance scanning section (ii) to the mirror part via the resonance scanning section having (a) the actuator part and (b) the beam part.
However, in the above-described structure of the vari-focal mirror, the resonance scanning section is also formed as a layered structure, in which the conductive base material supports the piezoelectric film and a resonance scanner electrode, and the mirror driving wire passing through the resonance scanning section also extends on the piezoelectric film. Specifically, in consideration of element size reduction, the mirror driving wire is simply put on the piezoelectric film. In such case, when applying a voltage to the vari-focal mirror through the mirror driving wire, the voltage is also applied to the piezoelectric film that lies between the mirror driving wire and the conductive base material, thereby causing a warpage or deformation of the piezoelectric film and altering the resonance frequency of the resonance scanning section, which is problematic to the optical scanner.
As a resolution to such a problem, the area size of the resonance scanning section may be expanded to protrude to an outside of the actuator part, and the mirror driving wire may be positioned at an outside of the resonance scanner electrode, and the actuator part and the mirror driving wire may be insulated from each other. However, to expand the resonance scanning section, extra space is required, which makes it difficult to reduce the size of the optical scanner.